1. Technical Field
The present invention relates to a flame-retardant resin composition and a flame-retardant resin molded article which contain a resin mixed with flame-retardant particles.
2. Related Art
An external covering material for printers or copying machines requiring flame retardancy is made of blend materials of a polycarbonate (PC) resin/ABS resin, PC resin/polystyrene (PS) resin or the like, wherein a PC resin is used as a major component. Since a PC resin has disadvantages of high costs and poor workability, it is better to increase an ABS resin content in the blend material. In this case, however, it is particularly necessary to impart flame retardancy to the ABS resin.
There are bromine-based agents and phosphorous-based agents as flame retardancy-imparting materials which are principally used at present. However, both of them have an impact on the environment. As flame retardancy-imparting materials having environmental suitability, there are silicone-based materials, metal hydrates, nitrogen-based materials and the like. However, in blend materials of a polycarbonate resin/ABS resin (PS resin), each resin exhibits different selectivity in flame retardancy-imparting materials which can be used, so in practice it is difficult to find a flame retardancy-imparting material that can commonly be used with both the resins.
As flame retardants effective for polycarbonates there are organosiloxanes. As specific examples, (1) a PC copolymerized with a silicone (Example: EXL 9330, trade name, manufactured by GE Corporation) and (2) a PC to which a silicone is added (Example: POLYCA 876-20, trade name, manufactured by Sumitomo Dow SD Corporation) are known.
Also, (3) an ABS flame-retarded with magnesium hydroxide is known. In addition, (4) a material prepared by blending an ABS with a PC flame-retarded with a silicone copolymer (Example: AC 1070, trade name, manufactured by Idemitsu Kosan Corporation) is known.
However, these materials involve the following problems. The material (1) has poor flowability so that molding processability is poor as a covering material. The material (2) has poor flame retardancy stability, and the material (4) exhibits poor humidity stability. The material (3), which contains a metal hydroxide, requires a large amount of a flame retardancy-imparting material to be added in order to obtain flame retardancy, which leads to problems such as the lowering of the mechanical characteristics of the resin and deterioration of moldability.
The present inventors have studied blend materials of a PC flame-retarded with a silicone and a metal hydrate (magnesium hydroxide). As a result, it has been found that the magnesium hydroxide contained in the above-described ABS has a hydroxyl group and thus exhibits alkalinity, whereby the PC is hydrolyzed to cause a foaming phenomenon at the time of kneading the PC with the ABS. Besides, in order to impart flame retardancy to the ABS, it is required to add a large amount of magnesium hydroxide, whereby the kneading load of the resin composition is increased.